1. Field of the Invention
The invention relates to an electrical power transfer device like a slipring or rotary joint. Sliprings are used to transfer electrical power between rotating parts of machines like wind power plants, CT scanners or electrical generators. There a brush, mainly including of electrically conductive material like a metal or carbon is sliding on a rotating cylindrical track of conductive material. Common materials for such tracks are steel or brass, sometimes being gold or silver-plated.
2. Description of Related Art
In the European patent application EP 0662736 A, a slipring is disclosed which includes of a plurality of wires of conductive material which are sliding in a V-groove of a sliding track of further conductive material. Due to the galvanic con-tact between the wires and the sliding track electric current can be transferred between the two parts rotating against each other. Such a slipring may only be used under moderate environmental conditions like in a building. It cannot be used under extreme environmental conditions like low ambient temperatures and high humidity. Under low temperatures, there may be a thin ice film on the sliding tracks which may prevent a contact by the brushes or which may cause at least significant contact noise. Furthermore, under low temperatures the oil, which is required to prevent high wear at the contacting surfaces, is too viscous to provide a sufficient lubrication. The high humidity may lead to a thin ice film with decreasing temperature and it further decreases the electrical isolation, which may lead to leakage currents and arcs on the surfaces.
The international patent application publication WO 2012/028992 discloses problems arising due to high heat developing under rotation of a slipring while transferring high currents. It further discloses a solution to handle high temperatures within the slipring by selecting specific materials.